If the locale is set to German (in my case by the environment variable LANG=de_DE.UTF-8) and I write a PDF-file using the QPdfWriter (or Qprinter) class in the PDF meta data ',' is used instead of the required '.' . (in German number fractions are indicated by ',' not by '.') Example:
/MediaBox [0 0 842,000000 1191,000000]
/MediaBox [0 0 842.000000 1191.000000]
I can fix this in the code by explicitly setting the locale to "C". However setting a certain locale should not cause PDF metadata to be compromised.